Question

Which of the following solutions has the same pH as a solution containing 0.010 M HNO3 and 0.020 M HClO (Ka = 2.9 ×10–8).

A. 0.010 M HCl

B. 0.030 M HNO3

C. 0.030 M HClO

D. 0.010 M H2SO4 (Ka2 = 1.2 ×10–2)

The correct answer is A, but I don't know how. Thanks!

Answer 1

[H+] total = 0.01 + 0.02(ionized)

note that HClO has a low Ka value, will not ionize more than 2%, therefore 0.02 --> assume to be almost neglegible compared to 0.01

(actual answer will be something like --> 0.0100000001 or so, therefore, 0.01 is the final result we will use)

assume 0.02 --> almost nothing compared to 0.01 M

the

pH = -log(H) = -log(0.01) =2

nearest will be

A) 0.01 M of HCl

pH of HCl = -log(0.01) = 2

which is approx the value we got